Portable exercise monitoring devices are becoming increasingly popular as the public becomes aware of the value of periodic exercise activities. However, for many exercisers it is essential that exercise activities not be overdone. For example, it is important for an exerciser having a heart difficulty to have his heartbeat rate monitored during exercise. Various exercise monitoring devices are in existence for alerting a user that a predetermined heartbeat rate has been exceeded. Once such device is disclosed in my U.S. patent application Ser. No. 103,422. One problem with heartbeat sensors such as that described in the referenced patent application is if the sensor moves relative to a fixed position on the user's body, the heartbeat measured thereby becomes somewhat blurred and ambiguous. Thus, the actual time of occurrence of the heartbeat and the isolation of the various portions of a single heartbeat cycle becomes difficult. It is important that small portable heartbeat sensors maintain a fixed relationship with respect to the monitoring area on the user's body. A typical exercise monitoring device uses the user's fingertip as the monitoring point, and attempts to maintain the heartbeat sensor in a fixed relationship with respect to an area located underneath a lower portion of the user's fingertip as the user exercises. Several devices designed to accomplish that purpose are disclosed in the referenced patent application. Although those devices have been found to be satisfactory, the device provided by the present invention is a one-piece device which can be quickly and accurately positioned on the user's fingertip while at the same time being extremely compact and simple in design.